1 Field of the Invention
The present invention relates to a valve unit used in a two-liquid mixing tap unit or mixing faucet for mixing two different liquids, such as hot water and cold water, and a synthetic resin valve seat used with the valve unit.
2. Description of Related Art
In general, a hot and cold water mixing plug unit (two-liquid mixing tap unit) installed in a household lavatory includes a valve unit constructed to be able to mix hot water and cold water to provide warm water.
In such a valve unit used with the hot and cold water mixing plug unit, a fixed valving element equipped with an inflow hot water valve aperture, an inflow cold water valve aperture, and an outflow mixed water valve aperture is secured in a valve case. Furthermore, a movable valving element that is movably operated by an operating means, such as a handle, is accommodated in the valve case so that it comes in slidable contact with the fixed valving element. The valve unit is constructed such that, when the movable valving element is moved to a valve opening position by the operating mean, at least either the hot water valve aperture or the cold water valve aperture becomes in communication with the mixed water valve aperture through a communication aperture in the movable valving element. When the movable valving element is moved to a valve closing position by the operating means, the movable valving element closes the hot water valve aperture and the cold water valve aperture.
A conventionally known valve unit disclosed, for example, in Japanese Unexamined Patent Publication No. 8-200526 or Japanese Unexamined Patent Publication No. 8-14422, a ceramic valve seat is disposed on each slide contact surface of the fixed valving element and the movable valving element, respectively, thereby to improve the durability of the slide contact portions of the fixed valving element and the movable valving element so as to eventually improve the durability of a valve unit itself.
Regarding the ceramic valve seat used with the valve unit, however, the profile irregularity of the slide contact surface thereof directly influences water-tightness. For this reason, after a sintering and forming process, the slide contact surface is polished with high accuracy and provided with plating. Hence, the ceramic valve seats require extra processing steps, making them more expensive than other components of a valve unit. In particular, the ceramic valve seat disposed on the fixed valving element has a hot water valve aperture, a cold water valve aperture, and a mixed water valve aperture, so that the configuration thereof is complicated, making it more expensive than the ceramic valve seat disposed in the movable valving element.